Conventionally known is a detection apparatus that is capable of detecting connection of an unauthorized apparatus to a communication line in a system in which a plurality of communication apparatuses perform communication via communication lines. JP 2014-143631A discloses an unauthorized connection detection system in which a predetermined voltage is applied to a communication line, a voltage on the communication line is detected, and it is determined whether or not a regular (authorized) tool is connected thereto based on the detected voltage.
Also, JP 2015-5829A discloses a connection detection apparatus for acquiring information on the waveform of a signal that is transmitted or received with a communication line, compares the acquired waveform with a normal communication waveform, and detects connection of an apparatus to the communication line in accordance with the comparison result.
In the unauthorized connection detection system in JP 2014-143631A, if the detected voltage is higher than a usual voltage by about a predetermined voltage, it is determined that a regular tool is connected to the communication line, but in a state in which a regular tool is connected thereto, it is not possible to detect unauthorized connections when an unauthorized apparatus is connected thereto.
In order to acquire information on the waveform of a signal, the connection detection apparatus in JP 2015-5829A needs an apparatus for measuring a signal voltage level at a temporal resolution that is sufficiently short compared to the transfer rate of an oscilloscope or the like, and thus, if such an apparatus is provided in a communication apparatus, then an issue arises that the size of the communication apparatus and its cost will increase.
The present invention was made in light of these circumstances, and an object of the present invention is to provide a communication system, a harness, and a detection apparatus that are capable of easily detecting connection of an unauthorized apparatus to a communication line.